The product of the avian sarcoma virus transformation gene (src) is a phosphoprotein with a molecular weight of 60,000 (p60src). It appears to act as a protein kinase as assayed by the transfer of gamma-32p from ATP to IgG in specific immune complexes. During the coming year we will attempt to complete the purification of p60src by using conventional biochemical techniques. Experiments will be undertaken to provide additional proof that p60src is a protein kinase. Finally, new phosphorylated cellular proteins will be examined to determine if they are the target of p60src phosphorylation.